In the production of such metals as zirconium, hafnium and titanium by Kroll reduction processes, zircon and rutile sands are first chlorinated in the presence of carbon to produce gaseous zirconium, hafnium, titanium and silicon tetrachlorides, which metals are then reduced with, e.g., magnesium. The sands are typically chlorinated in the presence of carbon at temperatures greater than about 800.degree. C. in fluidized beds. Non-volatile compounds, and particularly calcium and sodium salts, in the zircon and rutile sands eventually build up in the chlorinators and create "sticky" bed conditions which inhibit fluidization thus the residues in the chlorinators must be periodically pulled.
The zircon and rutile sands may also contain small amounts of other elements which are removed from the chlorinators in the residues. Thus the residues generally contain radium, scandium, yttrium and other transition metals, including metals from the rare earth and actinide series. Depending upon their compositions, these residues must be disposed of (at significant cost) as RCRA and low radioactive level wastes because of the presence of radioactive radium, thorium and uranium. Preferably, the volume of these wastes are minimized for permanent storage.
It has been recently proposed to recover scandium and yttrium from the chlorinator residues as saleable byproducts in order to recover at least some of the cost of disposing of the wastes. Yttrium is useful in advanced ceramics and superconductor applications. Scandium is useful in various laser applications. These proposals generally involve a rather complicated sequence of multistage solvent extractions and precipitations. Organic solvents may be employed to extract the metal values. Thus these proposed processes result in additional liquid waste streams which must be treated.